docs: def _final_frame_length(header, final_frame_bytes):
      """Calculates the length of a final ciphertext frame, given a complete header
      and the number of bytes of ciphertext in the final frame.
  
      :param header: Complete message header object
      :type header: aws_encryption_sdk.structures.MessageHeader
      :param int final_frame_bytes: Bytes of ciphertext in the final frame
      :rtype: int
      """
      final_frame_length = 4  # Sequence Number End
      final_frame_length += 4  # Sequence Number
      final_frame_length += header.algorithm.iv_len  # IV
      final_frame_length += 4  # Encrypted Content Length
      final_frame_length += final_frame_bytes  # Encrypted Content
      final_frame_length += header.algorithm.auth_len  # Authentication Tag
      return final_frame_length